Glycosidic inhibitors of melanogenesis from leaves of Passiflora edulis

Abstract

A new flavonoid glycoside, chrysin 6-C-β-rutinoside (chrysin α-L-rhamnopyranosyl-(1→6)-C-β-glucopyranoside; 2), and two new triterpene glycosides, (31R)-31-O-methylpassiflorine (7) and (31S)-31-O-methylpassiflorine (8), along with 14 known glycosides, including three flavonoid glycosides, 1, 3, and 4, six triterpene glycosides, 5, 6, and 9-12, three cyano glycosides, 13-15, and two other glycosides, 16 and 17, were isolated from a MeOH extract of the leaves of Passiflora edulis (passion flower; Passifloraceae). The structures of new compounds were elucidated on the basis of extensive spectroscopic analysis and comparison with literature data. Upon evaluation of compounds 1-17 against the melanogenesis in the B16 melanoma cells induced with α-melanocyte-stimulating hormone (α-MSH), three compounds, isoorientin (1), 2, and (6S,9R)-roseoside (17), exhibited inhibitory effects with 37.3-47.2% reduction of melanin content with no, or almost no, toxicity to the cells (90.8-100.2% cell viability) at 100 μM. Western blot analysis showed that compound 2 reduced the protein levels of MITF, TRP-1, and tyrosinase, in a concentration-dependent manner while exerted almost no influence on the level of TRP-2, suggesting that this compound inhibits melanogenesis on the α-MSH-stimulated B16 melanoma cells by, at least in part, inhibiting the expression of MITF, followed by decreasing the expression of TRP-1 and tyrosinase. In addition, compounds 1-17 were evaluated for their inhibitory effects against the EpsteinBarr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells.

Keywords: Glycosides; Melanogenesis inhibition; Passiflora edulis.